Genealogy reconstruction from short tandem repeat genotypes in an Amazonian population

We have reconstructed partial genealogies in a sample of 44 SW Amazonian Ro ndonian Surui, in which 45 dinucleotide short tandem repeat polymorphisms h ad previously been typed. The genotypes of 488 pairs of individuals having an age difference of 13 or greater were compared, and parentage was exclude d if a pair failed to share an allele at more than one locus. In order to t est the power of this method, we computed the expected distribution of the number of exclusionary loci for such pairs of unrelated individuals, as wel l as that for individuals with different degrees of relatedness, and compar ed it to the observed distribution. We estimated that the pairs compared co ntained similar to 20% of individual pairs with a first-cousin relation or closer. A total of 25 pairs were identified as possible parent-child. In th ree instances, we could identify two or more children having a common paren t; we computed a relatedness coefficient in order to establish whether the children were full or half sibs. The genealogies inferred show that instanc es of polygyny and polyandry (or, alternatively, serial mating), in additio n to apparent monogamy, can be found among the Surui. The Surui sample can be used as a model for paleoanthropological populations, in which the deter mination of relatedness can provide further insights into the social struct ure of past populations. We estimate that, depending on the history of the populations and the degree of inbreeding, 10-20 highly informative nuclear loci should be typed in order to infer genealogies with acceptable confiden ce. (C) 1999 Wiley-Liss, Inc.